Magnetic Downhole Tool And Related Subassemblies Having Mu-Metallic Shielding

ABSTRACT

Systems and related methods are disclosed that involve the use of a magnetic downhole assembly or a magnetic downhole tool. The assembly and tool include a mu-metal sleeve that is operable to isolate a magnetic field and a permanent magnet disposed within the mu-metal sleeve. The assembly and tool also include an actuator that is operable to selectively extend and retract the sleeve to alternatingly expose and shield the permanent magnet. A conveyance is operable to deploy the magnetic downhole assembly and tool to a selected location within a wellbore and a controller is communicatively coupled to the actuator and operable to generate a control signal that causes the actuator to extend or retract the permanent magnet from the mu-metal sleeve.

FIELD OF THE INVENTION

The disclosure relates to oil and gas exploration and production, and more particularly, but not by way of limitation to systems that employ magnetic shielding formed from a mu-metal to selectively shield a permanent magnet to control downhole systems.

DESCRIPTION OF RELATED ART

Hydrocarbons occur naturally in subterranean deposits and their extraction includes drilling a well. The well provides access to a production fluid that often contains crude oil and natural gas. Generally, drilling of the well involves deploying a drill string into a formation. The drill string includes a drill bit that removes material from the formation as the drill string is lowered to remove material from the formation and form a wellbore. After drilling and prior to production, a casing may be deployed in the wellbore to isolate portions of the wellbore wall and prevent the ingress of fluids from parts of the formation that are not likely to produce desirable fluids. After completion, a production string may be deployed into the well to facilitate the flow of desirable fluids from producing areas of the formation to the surface for collection and processing. Both the drill string and production string may include a variety of downhole tools. Such downhole tools may also be deployed by slickline or wireline conveyances that mechanically lower tools into a wellbore for testing and other tasks after the well has been formed.

A number of additional mechanisms may he included in drill strings and production strings to protect equipment within the wellbore and ensure consistent operation of such equipment. For example, valves and blow-out preventers may be installed to prevent rapid, excessive increases in pressure and to prevent backflow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic view of a producing well in which a magnetic downhole tool is deployed;

FIG. 2 illustrates a schematic view of a subterranean well in which a magnetic downhole tool is deployed from a slickline conveyance;

FIG. 3A is a side, cross-section of a magnetic tool in an un-actuated state;

FIG. 3B is a side, cross-section of the magnetic tool of FIG. 3A in an actuated state;

FIG. 3C is a perspective view of the magnetic tool of FIG. 3A in an actuated state;

FIG. 4A is a side, cross-section view of a blowout inhibitor that includes a magnetorheological fluid and a magnet actuator in an un-actuated state;

FIG. 4B is a side, cross-section view of the blowout inhibitor of FIG. 4A in an actuated state.

FIG. 5A is a side, cross-section view of a zone isolator that includes a magnetorheological fluid and a magnet actuator in an un-actuated state; and

FIG. 5B is a side, cross-section view of the zone isolator of FIG. 5A in an actuated state.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following detailed description of the illustrative embodiments, reference is made to the accompanying drawings that form a part hereof. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is understood that other embodiments may be utilized and that logical structural, mechanical, electrical, and chemical changes may be made without departing from the scope of the invention. To avoid detail not necessary to enable those skilled in the art to practice the embodiments described herein, the description may omit certain information known to those skilled in the art. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the illustrative embodiments is defined only by the appended claims.

In the drawings and description that follow, like parts are typically marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness.

The embodiments described herein relate to the systems, tools, and methods that include the use of a downhole tool that includes a permanent magnet and a mu-metallic shield. In an illustrative embodiment, a system for deploying such a downhole tool includes a downhole tool having a shielding sleeve operable to isolate a magnetic field, a permanent magnet disposed within the shielding sleeve, and an actuator. As referenced herein, the shielding sleeve is a sleeve that is operable to prevent the transmittance of a magnetic field. The actuator is operable to selectively extend and retract the magnet from the sleeve to expose and shield the magnet, respectively. The system also includes a conveyance to deploy the downhole tool to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal to the actuator to extend or retract the magnet.

The shielding sleeve may include one or more layers of a mu-metal. For example, the shielding sleeve may be a single layer of mu-metal or a plurality of layers. The layers may be arranged adjacent to one another or separated by an insulating layer. As referenced herein, a mu-metal is a metal selected from a range of nickel-iron alloys having relatively high magnetic permeability. An example of a mu-metal is an alloy composed of, for example, approximately 77% nickel, 16% iron, 5% copper and 2% chromium or molybdenum. Mu-metals are useful for shielding against static or low-frequency magnetic fields because of their high permeability—having typical relative permeability values of 80,000-100,000.

In an illustrative system, the actuator may be a hydraulic actuator and the control signal may be a hydraulic control signal, or the actuator may be a solenoid and the control signal may be an electric control signal. In another embodiment, the actuator may be a mechanical actuator actuated by a mechanical control signal, such as a tension applied to the conveyance. The conveyance may he a slickline, a wireline, a production tool string, a drilling tool string, an umbilical cable, or any other suitable conveyance.

According to another illustrative embodiment, a downhole tool includes a mu-metal sleeve operable to isolate a magnetic field and a permanent magnet disposed within the mu-metal sleeve. The tool also includes an actuator operable to extend and retract the mu-metal sleeve to selectively shield and expose the permanent magnet, respectively. The mu-metal sleeve may be formed from one or more layers of a nickel-iron alloy or a similar nickel alloy. In an embodiment in which the tool has multiple mu-metal layers, the layers may be disposed adjacent one another or separated by a non-magnetic insulating layer. The insulating layer may be air, a cloth layer, a plastic layer, a dielectric layer, or a layer of any other suitable material. The actuator may be a hydraulic actuator, a solenoid, or a mechanical actuator.

According to another illustrative embodiment, a method for deploying a permanent magnet in a wellbore includes providing a downhole tool having a mu-metal sleeve that is operable to isolate a magnetic field and a permanent magnet disposed within the mu-metal sleeve. The downhole tool also includes an actuator, which is operable to selectively extend and retract the permanent magnet to alternatingly expose and shield the permanent magnet using the mu-metal sleeve.

The method also includes coupling the downhole tool to a conveyance, providing a controller that is communicatively coupled to the actuator, and generating a control signal to cause the actuator to extend or retract the permanent magnet. The actuator may be a hydraulic actuator, an electrical actuator, and a mechanical actuator, and, correspondingly, the control signal may be a hydraulic control signal, an electric control signal, or a mechanical control signal. The conveyance that is coupled to the actuator may be a slickline, a wireline, a production tool string, a drill string, a production tool string or any other suitable conveyance. The method may further include exposing the permanent magnet to control the viscosity of a magnetorheological fluid or exposing the permanent magnet to orient a second tool within a wellbore.

As referenced herein, a magnetorheological fluid is a type of fluid whose properties, including, for example, viscosity, change in the presence of a magnetic field. For example, when a magnetorheological fluid is exposed to a magnetic field, the viscosity of the fluid may increase to the extent that it becomes a viscoelastic solid. Examples of magnetorheological fluids include a first composition including 20 wt. % carbonyl iron (CI) and fumed silica stabilizer (“Aerosil 200”) in silicone oil (OKS 1050); a second composition including 40 wt. % carbonyl iron (CI) and fumed silica stabilizer (“Aerosil 200”) in silicone oil (OKS 1050); a third composition including 20 wt. % carbonyl iron (CI) in silicone oil (OKS 1050); and a fourth composition including 40 wt. % carbonyl iron (CI) in silicone oil (OKS 1050).

Unless otherwise specified, any use of any form of the terms “connect,” “engage,” “couple,” “attach,” or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements and may also include indirect interaction between the elements described. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to”. Unless otherwise indicated, as used throughout this document, “or” does not require mutual exclusivity.

The various characteristics mentioned above, as well as other features and characteristics described in more detail below, will he readily apparent to those skilled in the art with the aid of this disclosure upon reading the following detailed description of the embodiments, and by referring to the accompanying drawings. Other means may be used as well.

The representative systems, methods, and tools may be used in any number of well and tool string configurations, including, for example, the configurations described below. Referring now to the figures, FIG. 1 shows an example of a production system 100 that includes a blowout inhibitor 124 and a plurality of isolators 104. The production system 100 includes a rig 116 atop the surface 132 of a well 101. Beneath the rig 116, the wellbore 108 is formed within the geological formation 106, which is expected to produce hydrocarbons. The wellbore 108 may be formed in the geological formation 106 using a drill string that includes a drill bit to remove material from the geological formation 106. The wellbore 108 in FIG. 1 is shown as being near-vertical, but may be formed at any suitable angle to reach a hydrocarbon-rich portion of the geological formation 106. As such, in an embodiment, the wellbore 108 may follow a vertical, partially vertical, angled, or even a partially horizontal path through the geological formation 106.

Following or during formation of the wellbore 108, a production tool string 112 may be deployed that includes tools for use in the wellbore 108 to operate and maintain the well. Such tools may be referred to as downhole tools. For example, the production tool string 112 optionally includes an artificial lift system to assist fluids from the geological formation to reach the surface 132 of the well 101. Such an artificial lift system may include an electric submersible pump 102, sucker rods, a gas lift system, or any other suitable system for generating a pressure differential. The pump 102 receives power from the surface 132 from a power transmission cable 110, which may also be referred to as an “umbilical cable.” In the embodiment of FIG. 1, the umbilical cable may also serve as a conveyance for other items within the production tool string 112, such as a magnetic downhole tool as described below with regard to FIGS. 3A-3C.

In a production environment, as shown in FIG, 1, production fluids 146 are extracted from the formation 106 and delivered to the surface 132 via the wellbore 108. As fluid 146 is transported to the surface 132, the fluid passes through a blowout preventer 142 and a fluid diverter 144 that diverts fluid 146 to a collection tank 140 for subsequent processing and refinement.

In such systems, a well operator may monitor the condition of the well 101 and components of the production tool string 112 to ensure that the well operates efficiently and to determine whether the production fluid 146 has desired properties. For example, an operator may want to determine that the production fluid 146 has a high hydrocarbon content and a low water content. In some cases, a well operator may determine that a portion of the formation 106 produces desirable fluids while another portion of the foundation produces undesirable fluids, each such portion of the formation may be referred to as a zone. An operator may similarly determine that different zones within a formation produce fluid at different rates, or that different zones have higher or lower hydrostatic pressure relative to one another. For example, the formation 106 may have a first zone 156 that interacts with the wellbore 108 downhole from a second zone 158. To account for such differing characteristics, an operator may include an isolator 104 for separating the first zone 156 from the second zone to allow for different rates of production or to allow, for example, production of fluid from the first zone 156 without allowing production from the second zone 158. Similarly, to prevent the ingress of fluids from a zone in the formation 106, the system 100 may include a casing 114 that restricts the communication of fluids between the formation 106 and wellbore 108.

In addition, the well operator may take steps to ensure that the pressure in the well does not increase beyond a predetermined threshold, and that pressure within the well or production string 112 does not increase at a rate that is faster than a predetermined rate. Rapid increases in pressure, which may be referred to herein as “pressure spikes” may damage equipment in the production string 112 that is subject to the pressure spike or stress other sealing elements that are designed to contain the well. To account for such pressure spikes and prevent damage to wellbore equipment, the production system 100 may include a blowout inhibitor 124 that prevents such pressure spikes from being transmitted to parts of the production string that are up-hole from, or closer to the surface than, the blowout inhibitor 124. The system 100 may also include a pressure sensor 148 to monitor pressure in the wellbore at or near the blowout inhibitor 124.

In an embodiment, a surface controller 120 may be communicatively coupled to the isolator 104 or blowout inhibitor 124 (either of which may be referred to as a “downhole component”) by the cable 110 or by a wireless communication protocol, such as mud-pulse telemetry or a similar communications protocol. The cable 110 may supply power to the downhole component and facilitate the transmission of data between the surface controller 120 and downhole component. In some embodiments, one or more of the downhole components may be permanently or semi-permanently deployed in the wellbore 108, and may include an on-board controller that functions autonomously or that communicates with the surface controller 120 via a wired or wireless communications protocol.

The production system 100 of FIG. 1 is deployed from the rig 116, which may be a drilling rig, a completion rig, a workover rig, or another type of rig. The rig 116 includes a derrick 109 and a rig floor 111. The production tool string 112 extends downward through the rig floor, through a fluid diverter 144 and blowout preventer 142 that provide a fluidly sealed interface between the wellbore 108 and external environment. The rig 116 may also include a motorized winch 130 and other equipment for extending the tool string 112 into the wellbore 108, retrieving the tool string 112 from the wellbore 108, and positioning the tool string 112 at a selected depth within the wellbore 108.

While the operating environment shown in FIG. 1 relates to a stationary, land-based rig 116 for raising, lowering and setting the tool string 112, in alternative embodiments, mobile rigs, wellbore servicing units (such as coiled tubing units, slickline units, or wireline units), and the like may be used to lower the tool string 112. Further, while the operating environment is generally discussed as relating to a land-based well, the systems and methods described herein may instead be operated in subsea well configurations accessed by a fixed or floating platform. Further, while the downhole components are shown as being deployed in a production environment, the downhole components may be similarly deployed in a drilling environment during the formation of the wellbore 108 and in slickline operations.

Referring now to FIG. 2, a magnetic downhole tool 270 that is analogous to the magnetic downhole tool of the illustrative embodiments described above is shown deployed in a slickline system 200. The deployment of the slickline tool string 215 is analogous in many respects to the deployment of the production tool string 112 of FIG. 1. For example, the slickline tool string 215 is deployed into a wellbore 208 formed in a formation 206. The tool string 215 is lowered into the wellbore 208 from a slickline conveyance 210 from a rig 216 that includes a platform 211 and derrick 209. The depth to which the tool string 215 is lowered is controlled by a motorized winch 230 mounted at the surface 232 and controlled by a surface controller 220, which may also be communicatively coupled to the tool 270. As described in more detail below, the magnetic downhole tool 270 may include a permanent magnet that can be selectively exposed and shielded.

The magnetic downhole tool 270 may therefore be lowered into the wellbore 208 in a shielded state and actuated to an exposed state to accomplish a number of downhole tasks. For example, the permanent magnet may be exposed to retrieve a stuck tool, a fragment thereof, or any other magnetic object from the wellbore. In another embodiment, the magnetic downhole tool 270 may be actuated and the magnet exposed to retrieve a plug 272 from a casing 214 in the wellbore 208, or to orient or otherwise position a second tool in the wellbore 208 relative to the magnet of the magnetic downhole tool 270. For example, the magnetic downhole tool 270 may be used to deliver and orient a second tool downhole, to orient a plug in a casing in the wellbore 208, or to move or shift a screen in a downhole environment.

FIGS. 3A-3C show an embodiment of a downhole tool 300 that is analogous to the magnetic downhole tool 270 described above with regard to FIG. 2. The tool 300 includes coupling 312 for coupling the downhole tool 300 to a conveyance, such as slickline cable, a wireline cable, or a tool string, and a shielding sleeve 304, which may be a mu-metal sleeve, as described above. The shielding sleeve 304 may be formed from a single layer of the mu-metal or by plurality of layers. In an embodiment, the shielding sleeve 304 includes a first layer 320 and a second layer 322 separated by an optional insulator 324 or insulating layer. In an embodiment that includes the insulator 324, the insulator 324 is formed from a material that is magnetically inert, such as a foam, cloth, a vacuum, air, a non-magnetic solid material, or a non-magnetic liquid layer. The shielding sleeve encloses a permanent magnet 302. The permanent magnet 302 includes a magnetized material that generates a persistent magnetic field. The magnetized material may he a ferromagnetic material, such as iron, nickel, cobalt, and alloys thereof. In an embodiment, the magnetized material is a magnetically processed alnico or ferrite.

The permanent magnet 302 is housed within the shielding sleeve 304 and is coupled to a piston 310 of an actuator 306 that is operable to extend the permanent magnet 302 from the shielding sleeve 304 in response to receiving an actuation signal from a controller, which may be a surface controller or an onboard controller. FIGS. 3B and 3C show the magnetic downhole tool 300 in an extended state in which the permanent magnet 302 protrudes from the shielding sleeve 304 to magnetically engage objects that are outside of the shielding sleeve 304.

In an embodiment, the actuator 306 may he actuated in a binary mode in which the piston 310 is either fully extended or fully retracted or in a continuously variable mode in which the piston 310 is extended only a specified distance. The actuator 306 may be a mechanical actuator, an electrical actuator, or a hydraulic actuator. In an embodiment in which the actuator 306 is a mechanical actuator, the actuator 306 may include a lever arm, gearing, ratchet extension, biasing spring, or some combination thereof to render the actuator 306 operable to extend the piston 310 in response to receiving a first mechanical actuation signal and to retract the piston 310 in response to receiving a second mechanical actuation signal. The first and second mechanical actuation signal may be an applied tension, a relaxed tension, a tension of a preselected magnitude, a series of applied tensions, or a combination thereof. In an embodiment, the first mechanical actuation signal and second mechanical actuation signal may be applied to the actuator 306 from a slickline conveyance.

In another embodiment, the actuator 306 may be a hydraulic actuator, such as a hydraulic chamber coupled to a hydraulic control line. The hydraulic chamber may receive a hydraulic control signal from a remote hydraulic controller or from a hydraulic control line that causes the piston 310 to extend and retract from the actuator 306. In another embodiment, the actuator 306 may be an electronic actuator, such as a solenoid, which may be coupled to an onboard controller or a surface-based controller that generates an actuation signal to cause the actuator 306 to extend and retract the piston 310 from the shielding sleeve 304.

In the actuated state shown in FIGS. 3B and 3C, the magnetic downhole tool 300 may be used for a number of downhole functions. For example, the magnetic downhole tool 300 may be deployed to retrieve a lost tool, broken equipment, or other magnetic debris from a wellbore. In another embodiment, the magnetic downhole tool 300 may be deployed to remove a plug from a wellbore casing, to shift a screen, or to assist with the delivery and orientation and installation of a second tool or other downhole equipment by attracting or repelling a magnetized surface toward or away front the magnetic downhole tool 300. For example, in an embodiment, the magnetic downhole tool 300 may be magnetically coupled to a second tool in an extended state, lowered into a wellbore to deliver the second tool to its intended location, actuated to transition the magnetic downhole tool 300 to a retracted state to decouple the second tool from the permanent magnet 302, and retrieved from the wellbore.

FIG. 4A shows a blowout inhibitor 400 that includes an actuator 406 that operates similar to actuator 306 of the magnetic downhole tool 300 described with regard to FIGS. 3A-3C. The blowout inhibitor 400 occupies a tubing segment 436 of the tool string and may also be referred to as a blowout inhibitor subassembly. The tool string may be a production string or any other type of tool string or conduit that delivers fluid from a formation to the surface. In the embodiment of FIG. 4A, the blowout inhibitor 400 is a magnetorheological blowout inhibitor that includes a reservoir 430. The reservoir 430 may be a cylindrical, or ring-shaped reservoir that is coupled to the interior of the tubing segment 436. A magnetorheological fluid 432 may be stored within the reservoir and released or forced into a flow path through the tubing segment 436. As referenced herein, the flow path refers to the path from a downhole opening of the tubing segment 436 upward to an upper opening of the tubing segment 436.

In an embodiment, the blowout inhibitor 400 also includes a controller 420 that is coupled to the reservoir 430 via a control line 422 and operable to actuate the release of magnetorheological fluid 432 from the reservoir 430. In an embodiment, the controller 420 includes or is coupled to a pressure sensor that monitors the pressure of fluid in the tool string and the rate of change of pressure in the tool string. The pressure sensors and controller 420 may be operable to monitor the static pressure at or below the sensor location to determine if the static pressure exceeds a predetermined pressure of if the static pressure is increasing at a rate that is faster than a predetermined rate of change. As referenced herein, either an increase in the static pressure beyond the predetermined pressure or an increase in the rate of change of the static pressure beyond the predetermined rate of change may be referred to as a “pressure spike.” The predetermined pressure and predetermined rate of change of pressure may be selected to correspond to pressure changes or rates of pressure change that are likely to increase the risk of equipment in the tool string that is upstream from the blowout inhibitor 400.

In an embodiment, the controller 420 is configured to detect a pressure spike and to cause the magnetorheological fluid 432 to be released from the reservoir 430 into the flow path in response to detection of a pressure spike. The detection of the pressure spike may also result in the transmission of an actuation signal from the controller 420 to a permanent magnet assembly 401 that is coupled to the controller 420 via the control line 422. The permanent magnet assembly 401 includes an enclosure 404 that includes a metallic shield. Like the metallic shields discussed above, the metallic shield may be formed from one or more layers of a mu-metal. One or more permanent magnets 402 are selectively extendable and retractable from the enclosure 404 by one or more synchronized actuators 406, each having a piston 410 that is coupled to the permanent magnet 402 and operable to extend and retract the permanent magnet 402. Each actuator 406 may therefore cause a piston 410 to extend and retract the permanent magnet 402 in response to an actuation signal received from the controller 420.

In an embodiment, the controller 420 may be replaced by a surface controller or other controller that is operable to monitor pressure within the tool string. As discussed above with regard to the actuator of the downhole tool of FIGS. 3A-3C, the actuator 406 may be a mechanical actuator, a hydraulic actuator, or an electronic actuator, and the actuation signal may be transmitted to the actuator 406 using any of the types of control lines and control signals discussed above. In the embodiment of FIGS. 4A and 4B, however, the actuator 406 is considered to be an electronic actuator, such as a solenoid, that receives an actuation signal from the controller 420 via an electronic control line 422. To generate a magnetic field across the flow path upon extension of the permanent magnet 402, a ferromagnetic member 408 may be placed at the center of the tubing segment 436 to facilitate the formation of a magnetic field between the permanent magnet 402 and the ferromagnetic member 408.

In another embodiment, the ferromagnetic member 408 may be omitted and two permanent magnets of opposing polarity may be placed across from each other in the enclosure 404, which may be separate enclosures, with each enclosure 404 and permanent magnet 402 occupying opposing sides of the tubing segment 436. In such an embodiment, extension of the permanent magnets 402 of opposing polarity will generate a magnetic field between the permanent magnets 402 across the flow path of the tubing segment 436.

FIG. 4B shows the blowout inhibitor 400 in an actuated state in which the system has been actuated in response to, for example, a pressure spike. In the actuated state, the controller 420 has transmitted actuation signals to the reservoir 430 and actuator 406. In response to receiving the actuation signal, the reservoir has released the magnetorheological fluid 432 into the flow path of the tubing segment 436. The magnetorheological fluid 432 may be released by any suitable release method. For example, the magnetorheological fluid 432 may be forced through a valve 440 into the flow path by a pump, by a collapse of the of reservoir 430, by a piston or other mechanism that forces the magnetorheological fluid 432 into the flow path, or by releasing a pressurized fluid into the reservoir 430 that displaces the magnetorheological fluid 432 into the flow path.

In the embodiment of FIG. 4B, the actuation signal has also caused the actuator 406 to extend the permanent magnet 402 from the enclosure 404. To prevent propagation of the pressure spike up-hole from the tubing segment 436, a magnetic field 438 is generated between the ferromagnetic member 408 and the extended permanent magnets 402. In an embodiment that does not include the ferromagnetic member 408, the magnetic field 438 may be generated between permanent magnets 402 of opposing polarity. As the magnetorheological fluid 432 flows into the magnetic field 438, interaction between the magnetic field and magnetorheological fluid 432 causes the magnetic fluid to form a visco-elastic solid, which effectively clogs the fluid flow path and forms a seal 434 that prevents the pressure spike from propagating upward and inhibits blowout. In an embodiment, a support structure that does not generally inhibit flow along the flow path in the absence of a pressure spike may be included in the tubing segment 436 to assist with formation of the seal 434. For example, a lattice, web, netting, or combination thereof may be deployed at the intended location of the seal 434 to provide additional anchor points for the magnetorheological fluid 432 as it begins to interact with the magnetic field 438 and solidify.

FIG. 5A shows a zone isolator 500 that includes an actuator 506 that operates similar to actuator 306 of the magnetic downhole tool 300 described with regard to FIGS. 3A-3C. The zone isolator 500 occupies a tubing segment 536 of the tool string and may also be referred to as a zone isolations subassembly. The tool string may be a production string or any other type of tool string that delivers fluid from a formation to the surface. In the embodiment of FIG. 5A, the zone isolator 500 is a magnetorheological zone isolator that includes a reservoir 530. The reservoir 530 may be a cylindrical, or ring-shaped reservoir that is coupled to the tubing segment 536 and operable to emit fluid to the exterior of the tubing segment 536. A magnetorheological fluid 532 may be stored within the reservoir 530 and released or forced into the fluid that is adjacent a permanent magnet assembly 501. As such, the reservoir 530 may be located above, below, or coincident with the permanent magnet assembly 501 depending on the direction of fluid flow.

In an embodiment, the zone isolator 500 also includes a controller 520 that is coupled to the reservoir 530 via a control line 522 and operable to actuate the release of magnetorheological fluid 532 from the reservoir 530 at the direction of a well operator. The controller 520 may be coupled to a surface controller via a wired or wireless communication interface to receive an actuation instruction from a well operator. In an embodiment, the controller 520 is configured to cause the magnetorheological fluid 532 to be released from the reservoir 530 adjacent to the permanent magnet assembly in response to an actuation instruction. The receipt of the actuation instruction may also result in the transmission of an actuation signal from the controller 520 to the permanent magnet assembly 501.

The permanent magnet assembly 501 includes an enclosure 504 that includes a metallic shield. Like the metallic shields discussed above, the metallic shield may be formed from one or more layers of a mu-metal. One or more permanent magnets 502 are selectively extendable and retractable from the enclosure 504 by one or more synchronized actuators 506, each having a piston 510 that is coupled to the permanent magnet 502 and operable to extend and retract the permanent magnet 502. Each actuator 506 may therefore cause a piston 510 to extend and retract the permanent magnet 502 in response to an actuation signal received from the controller 520.

In an embodiment, the controller 520 may be replaced by a surface controller or other controller that is operable to transmit an actuation instruction to the permanent magnet assembly 501 and reservoir 530. As discussed above with regard to the actuator of the downhole tool of FIGS. 3A-3C, the actuator 506 may be a mechanical actuator, a hydraulic actuator, or an electronic actuator, and the actuation signal may be transmitted to the actuator 506 using any of the types of control lines and control signals discussed above. In the embodiment of FIGS. 5A and 5B, however, the actuator 506 is considered to be an electronic actuator, such as a solenoid, that receives an actuation signal from the controller 520 via an electronic control line 522.

FIG. 5B shows the zone isolator 500 in an actuated state in Which the system has been actuated in response to an actuation instruction. In the actuated state, the controller 520 has transmitted actuation signals to the reservoir 530 and actuator 506. In response to receiving the actuation signal, the reservoir has released the magnetorheological fluid 532 adjacent the permanent magnet assembly 501. The magnetorheological fluid 532 may be released by any suitable release method, as described above with regard to FIG. 4B.

In the embodiment of FIG. 5B, the actuation signal has also caused the actuator 506 to extend the permanent magnet 502 from the enclosure 504. To prevent fluid communication between the wellbore zone above the tubing segment 536 and the wellbore zone below the tubing segment 536, a magnetic field 538 is generated between the wellbore wall 508 and the extended permanent magnets 502. As the magnetorheological fluid 532 flows through one or more valves 542 into the magnetic field 538 in the wellbore 508, interaction between the magnetic field 538 and magnetorheological fluid 532 causes the magnetic fluid to form a visco-elastic solid, which effectively forms a zone isolator 540 that prevents fluid interaction between the two wellbore zones. In an embodiment, a support structure that does not generally inhibit flow along the exterior of the tubing segment 536 may be included to assist with formation of the zone isolator 540. For example, a magnetically conductive lattice, web, netting, or combination thereof may be deployed at the intended location of the zone isolator 540 to strengthen the zone isolator and extend the magnetic field 538 by providing an anchor structure for the magnetorheological fluid 532 as it begins to interact with the magnetic field 538 and solidifies.

In addition to the illustrative embodiments described above, many examples of specific combinations are within the scope of the disclosure, some of which are presented below.

Example one: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal.

Example two: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The shielding sleeve is a mu-metal.

Example three: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The shielding sleeve comprises a mu-metal, and the mu-metal is a nickel-iron alloy.

Example four: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The actuator is a hydraulic actuator and the control signal is a hydraulic control signal.

Example five: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The actuator is a solenoid and the control signal is an electric control signal.

Example six: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The actuator is a mechanical actuator and the control signal is a mechanical control signal.

Example seven: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The system further includes a tubing segment having a fluid flow path therethrough and a reservoir coupled to the controller and having a magnetorheological fluid disposed therein. The reservoir is operable to disperse the magnetorheological fluid into the fluid flow path in response to the control signal.

Example eight: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The system further includes a tubing segment having a fluid flow path therethrough and a reservoir coupled to the controller and having a magnetorheological fluid disposed therein. The reservoir is operable to disperse the magnetorheological fluid into the fluid flow path in response to the control signal. The magnetic downhole assembly is operable to extend the permanent magnet adjacent the fluid flow path to generate a magnetic field across the fluid flow path in response to the control signal.

Example nine: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The system further includes a tubing segment having a fluid flow path therethrough and a reservoir coupled to the controller and having a magnetorheological fluid disposed therein. The reservoir is operable to disperse the magnetorheological fluid into the fluid flow path in response to the control signal. The magnetic downhole assembly is operable to extend the permanent magnet adjacent the fluid flow path to generate a magnetic field across the fluid flow path in response to the control signal. The system also includes a ferromagnetic member.

Example ten: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The system further includes a tubing segment having a fluid flow path therethrough and a reservoir coupled to the controller and having a magnetorheological fluid disposed therein. The reservoir is operable to disperse the magnetorheological fluid into the fluid flow path in response to the control signal. The magnetic downhole assembly is operable to extend the permanent magnet adjacent the fluid flow path to generate a magnetic field across the fluid flow path in response to the control signal. The system also includes a pressure sensor coupled to the controller. The controller is operable to generate the control signal in response to determining that a pressure at the pressure sensor is greater than a predetermined pressure.

Example eleven: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The system further includes a tubing segment having a fluid flow path therethrough and a reservoir coupled to the controller and having a magnetorheological fluid disposed therein. The reservoir is operable to disperse the magnetorheological fluid into the fluid flow path in response to the control signal. The magnetic downhole assembly is operable to extend the permanent magnet adjacent the fluid flow path to generate a magnetic field across the fluid flow path in response to the control signal. The system also includes a pressure sensor coupled to the controller. The controller is operable to generate the control signal in response to determining that a pressure at the pressure sensor is increasing at a rate that is greater than a predetermined rate.

Example twelve: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The system further includes a tubing segment having a fluid flow path therethrough and a reservoir coupled to the controller and having a magnetorheological fluid disposed therein. The reservoir is operable to disperse the magnetorheological fluid into the fluid flow path in response to the control signal. The magnetic downhole assembly is operable to extend the permanent magnet adjacent the fluid flow path to generate a magnetic field across the fluid flow path in response to the control signal. The system also includes a lattice disposed in the fluid flow path proximate the magnetic downhole assembly.

Example thirteen: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The system further includes a tubing segment having a fluid flow path therethrough and a reservoir coupled to the controller and having a magnetorheological fluid disposed therein. The reservoir is operable to disperse the magnetorheological fluid into the fluid flow path in response to the control signal. The magnetic downhole assembly is operable to extend the permanent magnet adjacent the fluid flow path to generate a magnetic field across the fluid flow path in response to the control signal. The system also includes a web disposed in the fluid flow path proximate the magnetic downhole assembly.

Example fourteen: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The system further includes a tubing segment having a fluid flow path therethrough and a reservoir coupled to the controller and having a magnetorheological fluid disposed therein. The reservoir is operable to disperse the magnetorheological fluid into the fluid flow path in response to the control signal. The magnetic downhole assembly is operable to extend the permanent magnet adjacent the fluid flow path to generate a magnetic field across the fluid flow path in response to the control signal. The system also includes netting in the fluid flow path proximate the magnetic downhole assembly.

Example fifteen: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The system further includes a tubing segment and a reservoir coupled to the controller. The reservoir includes a magnetorheological fluid disposed therein, and is operable to disperse the magnetorheological fluid adjacent the magnetic downhole assembly between an exterior surface of the tubing segment and a wellbore wall in response to the control signal.

Example sixteen: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The system further includes a tubing segment and a reservoir coupled to the controller. The reservoir includes a magnetorheological fluid disposed therein, and is operable to disperse the magnetorheological fluid adjacent the magnetic downhole assembly between an exterior surface of the tubing segment and a wellbore wall in response to the control signal. The magnetic downhole assembly is operable to extend the permanent magnet to generate a magnetic field about the external exterior surface of the tubing segment in response to the control signal.

Example seventeen: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The system further includes a tubing segment and a reservoir coupled to the controller. The reservoir includes a magnetorheological fluid disposed therein, and is operable to disperse the magnetorheological fluid adjacent the magnetic downhole assembly between an exterior surface of the tubing segment and a wellbore wall in response to the control signal. The controller is operable to generate the control signal in response to receiving an actuation instruction from an operator.

Example eighteen: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The system further includes a tubing segment and a reservoir coupled to the controller. The reservoir includes a magnetorheological fluid disposed therein, and is operable to disperse the magnetorheological fluid adjacent the magnetic downhole assembly between an exterior surface of the tubing segment and a wellbore wall in response to the control signal. The system also includes a lattice disposed about the external exterior surface of the tubing segment proximate the magnetic downhole assembly.

Example nineteen: A system for operating a magnetic downhole assembly including a magnetic downhole assembly having a shielding sleeve that is operable to isolate a magnetic field. The system also includes a permanent magnet disposed within the shielding sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. In addition, the system includes a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore and a controller communicatively coupled to the actuator and operable to generate a control signal. The system further includes a tubing segment and a reservoir coupled to the controller. The reservoir includes a magnetorheological fluid disposed therein, and is operable to disperse the magnetorheological fluid adjacent the magnetic downhole assembly between an exterior surface of the tubing segment and a wellbore wall in response to the control signal. The system also includes a web disposed about the external exterior surface of the tubing segment proximate the magnetic downhole assembly.

Example twenty: A magnetic downhole tool includes a mu-metal sleeve operable to isolate a magnetic field, a permanent magnet disposed within the mu-metal sleeve, and an actuator operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet.

Example twenty-one: A magnetic downhole tool includes a mu-metal sleeve operable to isolate a magnetic field, a permanent magnet disposed within the mu-metal sleeve, and an actuator operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The mu-metal sleeve comprises a plurality of layers of mu-metal.

Example twenty-two: A magnetic downhole tool includes a mu-metal sleeve operable to isolate a magnetic field, a permanent magnet disposed within the mu-metal sleeve, and an actuator operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The mu-metal sleeve comprises a plurality of layers of mu-metal, and the layers of mu-metal are separated by at least one insulating layer.

Example twenty-three: A magnetic downhole tool includes a mu-metal sleeve operable to isolate a magnetic field, a permanent magnet disposed within the mu-metal sleeve, and an actuator operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The mu-metal sleeve comprises a plurality of layers of mu-metal. The mu-metal is a nickel-iron alloy.

Example twenty-four: A magnetic downhole tool includes a mu-metal sleeve operable to isolate a magnetic field, a permanent magnet disposed within the mu-metal sleeve, and an actuator operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The actuator is a hydraulic actuator.

Example twenty-five: A magnetic downhole tool includes a mu-metal sleeve operable to isolate a magnetic field, a permanent magnet disposed within the mu-metal sleeve, and an actuator operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The actuator is a solenoid.

Example twenty-six: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve.

Example twenty-seven: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve. The mu-metal comprises a nickel-iron alloy.

Example twenty-eight: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve. The actuator is a hydraulic actuator and generating the control signal comprises generating a hydraulic control signal.

Example twenty-nine: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve. The actuator is a solenoid and the control signal is an electric control signal.

Example thirty: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve. The actuator is a mechanical actuator and generating the control signal includes generating a mechanical control signal.

Example thirty-one: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve. The method also includes coupling the magnetic downhole tool to a slickline conveyance and positioning the downhole tool at a selected location in a wellbore.

Example thirty-two: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve. The method further includes coupling the magnetic downhole tool to a wireline conveyance and positioning the downhole tool at a selected location in a wellbore.

Example thirty-three: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve. The method also includes coupling the magnetic downhole tool to a tool string and positioning the downhole tool at a selected location in a wellbore.

Example thirty-four: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve. The method also includes exposing the permanent magnet to control the viscosity of a magnetorheological fluid.

Example thirty-five: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve. The method also includes exposing the permanent magnet to orient a second tool within a wellbore.

Example thirty-six: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve. The method also includes exposing the permanent magnet to remove a plug from a wellbore casing.

Example thirty-seven: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve. The method also includes exposing the permanent magnet and manipulating the magnetic downhole tool to adjust the position of a screen.

Example thirty-eight: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve. The method also includes exposing the permanent magnet and manipulating the magnetic downhole tool to adjust the position of a second downhole tool.

Example thirty-nine: A method for operating a magnetic downhole tool includes providing a magnetic downhole tool comprising a mu-metal sleeve that is operable to isolate a magnetic field. The magnetic downhole tool also includes a permanent magnet disposed within the mu-metal sleeve and an actuator. The actuator is operable to selectively extend and retract the sleeve to selectively expose and shield the permanent magnet. The method also includes providing a controller that is communicatively coupled to the actuator and generating a control signal to cause the actuator to extend or retract the mu-metal sleeve. The method also includes exposing the permanent magnet to couple permanent magnet to a second downhole tool, delivering the second downhole tool to a selected location, and retracting the permanent magnet.

It will be understood that the above description of preferred embodiments is given by way of example only and that various modifications may be made by those skilled in the art. The above specification, examples, and data provide a complete description of the structure and use of exemplary embodiments of the invention. Although various embodiments of the invention have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of the claims. 

1. A system of operating a magnetic downhole assembly comprising: a magnetic downhole assembly having: a shielding sleeve operable to isolate a magnetic field; a permanent magnet disposed within the shielding sleeve, the permanent magnet being coupled to a piston; and an actuator operable to selectively extend and retract the piston from the shielding sleeve so as to selectively expose and shield the permanent magnet; a conveyance operable to deploy the magnetic downhole assembly to a selected location within a wellbore; and a controller communicatively coupled to the actuator and operable to generate a control signal.
 2. The system of claim 1, wherein the shielding sleeve comprises a mu-metal.
 3. The system of claim 1, wherein the actuator is selected from the group consisting of a hydraulic actuator, an electric actuator, and a mechanical actuator.
 4. The system of claim 1, further comprising: a tubing segment having a fluid flow path therethrough; a reservoir coupled to the controller and having a magnetorheological fluid disposed therein, the reservoir being operable to disperse the magnetorheological fluid into the fluid flow path in response to the control signal.
 5. The system of claim 4, further comprising a pressure sensor coupled to the controller, wherein the magnetic downhole assembly is operable to extend the permanent magnet adjacent the fluid flow path to generate a magnetic field across the fluid flow path in response to the control signal, and wherein the controller is operable to generate the control signal in response to determining that a pressure at the pressure sensor is increasing at a rate that is greater than a predetermined rate.
 6. The system of claim 1, further comprising a tubing segment and a reservoir coupled to the controller, wherein the reservoir comprises a magnetorheological fluid disposed therein, and wherein the reservoir is operable to disperse the magnetorheological fluid adjacent the magnetic downhole assembly between an exterior surface of the tubing segment and a wellbore wall in response to the control signal.
 7. The system of claim 6, wherein the magnetic downhole assembly is operable to extend the permanent magnet to generate a magnetic field about the external exterior surface of the tubing segment in response to the control signal.
 8. A magnetic downhole tool comprising: a mu-metal sleeve operable to isolate a magnetic field; a permanent magnet disposed within the mu-metal sleeve, the permanent magnet coupled to a piston; and an actuator, the actuator being operable to selectively extend and retract the piston from the mu-metal sleeve so as to selectively expose and shield the permanent magnet.
 9. The magnetic downhole tool of claim 8, wherein the mu-metal sleeve comprises a plurality of layers of mu-metal.
 10. The magnetic downhole tool of claim 9, wherein the layers of mu-metal are separated by at least one insulating layer.
 11. The magnetic downhole tool of claim 8, wherein the actuator is selected from the group consisting of a hydraulic actuator, a solenoid, and a mechanical actuator.
 12. A method of operating a magnetic downhole tool, the method comprising: providing a magnetic downhole tool comprising a mu-metal sleeve operable to isolate a magnetic field, a permanent magnet disposed within the mu-metal sleeve, the permanent magnet coupled to a piston, and an actuator, the actuator being operable to selectively extend and retract the piston from the mu-metal sleeve so as to selectively expose and shield the permanent magnet; providing a controller, the controller being communicatively coupled to the actuator; and generating a control signal to cause the actuator to extend or retract the metal sleeve.
 13. The method of claim 12, wherein the mu-metal comprises a nickel-iron alloy.
 14. The method of claim 12, wherein the step of generating the control signal is selected from the group consisting of generating a hydraulic control signal, generating an electric control signal, and generating a mechanical control signal.
 15. The method of claim 12, further comprising coupling the magnetic downhole tool to a conveyance and positioning the downhole tool at a selected location in a wellbore, wherein the conveyance is selected from the group consisting of a slickline, a wireline, and a tool string.
 16. The method of claim 12, further comprising exposing the permanent magnet to control the viscosity of a magnetorheological fluid.
 17. The method of claim 12, further comprising exposing the permanent magnet to remove a plug from a wellbore casing.
 18. The method of claim 12, further comprising exposing the permanent magnet and manipulating the magnetic downhole tool to adjust the position of a screen.
 19. The method of claim 12, further comprising exposing the permanent magnet and manipulating the magnetic downhole tool to adjust the position of a second downhole tool.
 20. The method of claim 12, further comprising exposing the permanent magnet to couple permanent magnet to a second downhole tool, delivering the second downhole tool to a selected location, and retracting the permanent magnet. 